1. Field of the Invention
The present invention relates to a surface light source device for use with back-light or the like for back-lighting for a transmissive display panel, and more particularly to air-cooled structure for a surface light source device containing lamps for bringing about heat evaluation.
2. Description of Related Art
A display panel using liquid crystal or the like for an electro-optical substance as a large-sized flat display as a replacement for the CRT has been positively developed in recent years.
The display panel is not of a active light emission type, but modulates external light to display a screen view. The display panel is roughly divided into two types a transmission type and a reflection type. In the case of the transmission type, a surface light source device is arranged on the back of the display panel for back-lighting.
A surface light source device which is used as a back-light for alarge-sized display panel contains lamps consisting of a large number of fluorescent tubes or the like which generate a large amount of heat. This heat raises the temperature of the display panel to change the electro-optical characteristics of the liquid crystal that is used as electro-optical substance, thus deteriorating the image quality. Also, the atmospheric temperature within the back-light rises to decrease the luminous efficiency of the fluorescent tubes, causing the a deterioration in brightness. For this reason, forced cooling using air-cooling fans or the like becomes indispensable in a large-sized back-light. If, however, an air-cooling fan is used, dust is whirled up to adhere to the surface of lamps or a diffuser panel disposed thereon, thus deteriorating the uniformity of brightness of the surface light source device.
If dust stuck on the lamps and the diffuser panel is visually recognized by an observer through a transmissive display panel, the image quality will be noticeably deteriorated.